Compressed air operated engines arc used in a number of applications. Primarily it is herein related to engines of displacement type, such as lamella engines having a wing provided rotor, but the invention can also be applied to turbine engines. In certain applications such engines operate using a shifting torque load. This is for example the case at hand tools such as a angle grinder, other grinding machines, and brushing tools as well as drilling machines. See for example the grinding machine according to U.S. Pat. No. 3,767,332 (Wickham et al).
By means an adjustable air valve the addition of air from the compressed air system is adjusted to the machine in such a way that a desired rotation speed is obtained, herein called the idling rotation speed. If no further means for regulating the rotation speed is at hand, the rotation speed will decrease at the adding of a load to the engine proportional to the torque added.
This is generally not wanted but one wants to maintain a substantially constant rotation speed regardless of the torque load. It is hereby known to arrange rotation speed regulating means of the centrifugal type, cf. the above mentioned patent publication. In these the throttling of ingoing air is adjusted dependent upon the position of rotating weights in the regulating means so that a decreasing rotation speed can be counteracted as the position of the weights is allowed to determine the throttling of the air added. Such a rotation speed regulating means will, however, become complicated and has not found any widespread use.
It is previously known from EP-A1-0 575 301 a speed regulator for compressed air operated high speed turbines, which regulator comprise a valve element which is arranged to control the flow of compressed air through the inlet channel as well as a piston means activating said valve element, which piston means is influenced by a speed related control pressure. The control pressure is obtained from an air flow which is led to the idling nozzle and which passes the turbine wheel before it flows to the piston means. The control pressure is determining how much the piston means is able to keep the valve element in an open position against a spring load and how much the air flow to the turbine wheel is throttled. The construction demands narrow tolerances, cooperating pistons provided with sealings, and is farther dependent on the characteristics of the pressure spring. These elements combined leads to a device sensitive to operational disturbances, as well as expensive to produce.
What has been said above has been related to machinery operated using a pressurized gas. In practise air, the expansion of which above a certain pressure fall provides for the work. This can be expressed as the rotation speed multiplied with the torque provided. At a constant addition of airt thus an increased torque will lead to a decreased rotation speed. A corresponding relationship occurs also at engines operated by a liquid, which provides a work by means of a pressure fall in a flow.
The regulating valve according to the present invention can thus be applied at liquid operated engines provided the liquid is not added in a forced controlled volume per time unit. Many hydraulic engines are, however, operated by pumps the flow of which can be adjusted to a constant value and if such a one operates a hydraulic engine of the displacement type an increase of the load of the engine will not lead to a lower rotation speed but instead a higher pressure of the liquid, resulting in a larger resistance in the pump and thereby a larger work provided. At hydraulic engines of the non-displacement type and operation in another way than by means of a displacement pump, for example by means of a liquid under pressure from a pressure accumulator, however, the regulating valve according to the invention may be applicable even within the hydraulic field.